A finite element analysis of an axisymmetrically loaded orthotropic shell of revolution

The objective of this study was to develop a finite element matrix method of analysis for symmetrically loaded orthotropic shells of revolution using closed form elasticity solutions for the element. A computer program for structural analysis was developed based on this method.

The program was used to analyze orthotropic cylindrical shells with edge loads, orthotropic spherical shells with edge loads, and pressurized ellipsoidal shells.

For the ellipsoidal shells, the ratio of the major to minor axis (a/b) varied from 0.2 to 1.8. The orthotropic materials used had ratios of Young's modulus in the meridional direction to Young's modulus in a direction tangent to a parallel circle (E₁/E₂) that ranged from 0.2 to 1.8.

For the structures and orthotropic materials studied, it was found that the edge effect, as signified by the meridional moment, was affected by the Young's moduli ratio E₁/E₂, the radius of curvature R₂ in the plane containing a normal to the shell surface and a tangent to a parallel circle, and Poisson's ratio v₂, the latter being more prominent for large E₁/E₂ values. The range of the E₁/E₂ ratio caused the meridional edge moment to double, increasing as the E₁/E₂ ratios increased from 0.2 to 1.8, for pressurized ellipsoidal shells. The meridional edge moment more than doubled as the ellipsoidal axes ratio, a/b, ranged from 0.2 to 1.8.     

The assessment of heat radiation

Approximately 900 climatic chamber experiments were performed with 16 male subjects to study the thermal strain at climates including increased heat radiation. Based on the reactions of heart rate, rectal temperature and sweat rate, a heat stress index was developed for the assessment of climates with effective heat radiation intensities up to 1400 W m⁻². The index considers different combinations of dry air temperature (5–55°C), globe temperature (25–76°C), mean radiant temperature (25–160°C), air velocity (0.5–2.0 m s⁻¹), clothing, physical work load and directions of radiation and air flow.

The index integrates combinations of the variables producing the same degree of thermal strain into a single value. This value indicates the temperature of the physiologically equivalent climate in which air and radiant temperature are equal. It can be determined from a simple formula or from correspondent graphs.

In comparison, the international recommended heat stress indices are less capable to evaluate heat radiation correctly. The incorporation of the new partial index into the used indices may improve substantially their physiological validity in the assessment of climates with radiant heat stress.

Relevance to industry

The goal of this paper is to provide an improved assessment of thermal stress in working environments in which heat radiation is an important heat stress factor.     

ZrO2氧传感器封接料开裂失效分析及改进

针对氧化锆(ZrO2)氧传感器封接料失效机理,提出了在传感器加热电路上增加预热功能,通过仿真和试验的方法验证了改进措施的有效性.仿真分析的结果表明:温度变化幅度为200℃时应力状态较温度变化400℃时的应力降低幅度约为40%.通过试验样件验证表明,传感器在进行了576次启动热应力试验后,封接料状态良好,未开裂,表明加热电路增加预热功能后降低了热应力冲击强度,增加预热电路后,传感器有效避免了使用中出现封接料开裂故障.     

Bifurcation, pre- and post-buckling analysis of frame structures

A procedure is developed for investigating the stability of complex structures that consist of an assembly of stiffened rectangular panels and three-dimensional beam elements. Such panels often form one of the basic structural components of an aircraft or ship structure. In the present study, the stiffeners are treated as beam elements, and the panels between them as thin rectangular plate elements, which may be subject to membrane and/or bending and twisting actions.

The main objective of the study is the determination of the critical buckling loads and the generation of the complete force-deformation behavior of such structures within a specified load range, based on the use of a computer program developed for this purpose. The present formulation can trace through the postbuckling or post limit behavior whether it is of an ascending or descending type. A limit load extrapolation technique is automatically initiated within the computer program, when the stability analysis of an imperfect or laterally loaded structure is being carried out.

The general approach to the solution of the problem is based on the finite element method and incremental numerical solution techniques. Initially, nonlinear strain-displacement relations together with the assumed displacement functions are utilized to generate the geometric stiffness matrices for the beam and plate elements. Based on energy methods and variational principles, the basic expressions governing the behavior of the structure are then obtained. In the incremental solution process, the stiffness properties of the structure are continuously updated in order to properly account for large changes in the geometry of the structure.

The computer program developed during the course of this study is referred at as GWU-SAP, or the George Washington University Stability Analysis Program.     

Computer simulation of electric multizone tube furnaces

The paper presents the numerical model and computer program of calculations allowing the electric multizone tube furnace to be simulated. The program allows calculation of temperature distribution in thermally unsteady-state status in thermal insulation of the furnace and in the heating chamber. The program also enables the longitudinal distribution of temperature in the furnace to be calculated. The calculations involve the multilayer thermal insulation and change in physical properties of insulating materials and heat transfer coefficients with temperature.     

Vibration analysis of laminated anisotropic shells of revolution

An efficient computational procedure is presented for the free vibration analysis of laminated anisotropic shells of revolution, and for assessing the sensitivity of their response to anisotropic (nonorthotropic) material coefficients. The analytical formulation is based on a form of the Sanders-Budiansky shell theory including the effects of both the transverse shear deformation and the laminated anisotropic material response. The fundamental unknowns consist of the eight stress resultants, the eight strain components, and the five generalized displacements of the shell. Each of the shell variables is expressed in terms of trigonometric functions in the circumferential coordinate and a three-field mixed finite element model is used for the discretization in the meridional direction.The three key elements of the procedure are: (a) use of three-field mixed finite element models in the meridional direction with discontinuous stress resultants and strain components at the element interfaces, thereby allowing the elimination of the stress resultants and strain components on the element level; (b) operator splitting, or decomposition of the material stiffness matrix of the shell into the sum of an orthotropic and nonorthotropic (anisotropic) parts, thereby uncoupling the governing finite element equations corresponding to the symmetric and antisymmetric vibrations for each Fourier harmonic; and (c) application of a reduction method through the successive use of the finite element method and the classical Bubnov-Galerkin technique.The potential of the proposed procedure is discussed and numerical results are presented to demonstrate its effectiveness.     

Communication interface in a physical simulator for robotic palletization

This paper addresses the issues relating to the communication channels in a physical simulator for flexible automation of a palletization task. The simulator used in our work involves an IBM-7545 robot, a personal computer and an Allen-Bradley Programmable Logic Controller (PLC). The communications relating to the Robot/PC interface and the PLC/PC interface are discussed.

The palletization station design requires that decisions on pallet pattern are made dynamically by a program running on the personal computer. The Robot/PC communication interface is necessary to transmit these decisions to the robot controller for execution. This communication is to be achieved using BASIC language and AML 4.1 as the software platforms.

The PLC has the task of controlling the transport of the boxes coming to the palletization station. The program for deciding the pallet pattern, running on the personal computer, needs real-time information on the counts of boxes of different sizes that are arriving for palletization. The PLC/PC interface serves to provide this information.     

Interactive modeling system for bridges

The modeling system described in this paper was developed in conjunction with the computer program called STACRB that was developed in the CURT research project at the University of Pennsylvania. In essence, the STACRB program utilized the method of finite elements to analyze the static behavior of horizontally curved and straight aligned bridge structures.

The modeling system communicates with the user through a problem oriented language. The commands in this language allow the user to define the parameters that characterize the structure, modify an already existing structure, or inquire about the results of analysis already completed for a structure. The commands are entered in free format and are executed interpretively, thus allowing the user to communicate with the system in a conversational mode. The user may also enter the command on punched cards and execute the routine as a non-conversational batch job. The modeling system can be used to either control the analysis or operate independently from it. In the former case, the modeling system synthesizes the structure, then calls on the STACRB program to analyze it. When the analysis is completed, the control is returned to the modeling system to interpret the results of the analysis according to the commands supplied by the user. In the latter case, the results from the modeling procedure alone are punched onto cards which may subsequently be inputed to the analysis routine.

The modeling system also includes facilities for graphical displays of components of the designed structure such as structure geometry and element discretization or results of analysis such as nodal deflections, reactions and element stresses. The displays may be produced either on the line printer for conversational purposes or on a CALCOMP plotter.

The overall increased efficiency introduced by the modeling system in the analysis/design cycle of a bridge structure is quite significant.     

Fracture mechanics J-integral calculations in thermo-elasto-plasticity

A finite element post-processor has been developed to calculate an incremental plasticity-based J-integral for fracture mechanics evaluations. The post-processor accounts for elastic-plastic deformations and thermal strains. The ADINA finite element computer program, with minor modifications by Babcock and Wilcox, was used with the Ramberg-Osgood stress-strain law and provides through its “porthole” files the required results of stresses, strains, displacements, and elastic and plastic strain energies.

The numerical results of the post-processor indicate that the thermal J-integral, which consists of a line integral for the isothermal case and an additional area integral for the thermal effect, can be considered path-independent even in the presence of plastic and thermal strains.     

Dynamic optimization of framed structures

An analytical procedure for the determination of the least weight structure which satisfies a specific frequency requirement plus upper and lower bounds on the design variables is presented. The design algorithm is an iterative solution of the Kuhn-Tucker optimality criterion. The procedure is to modify an existing design to first obtain the correct structural frequency and then, while the frequency is held constant, to minimize the weight. This is accomplished using gradient equations derived in matrix notation for direct application to the finite element method of analysis.

The most important features of the algorithm are: (a) a small number of design iterations are needed to reach optimal or near-optimal design, (b) structural elements with a wide variety of size stiffness may be used.

The procedure has been completely automated in a computer program. Results of two numerical examples show that the method is convergent and that optimized configurations can be determined in as few as 10 redesign cycles.     

An approximate algorithm for the reanalysis of structures by the finite element method

An approximate computational algorithm is derived which permits a refined element analysis to be altered on a small capacity computer. The intent of the algorithm is to permit frequent design changes on any small computing machine where the computer cost is low and the machine-designer interaction is essentially instantaneous.

The method is based upon the dynamic normal mode method and upon an accompanying solution technique known as ·dynamic relaxation”. Geometric and material alterations, including the effects of material nonlinearities, are permissible design changes within the normal mode approach. The design alteration leads to a system of uncoupled nonlinear equations whose numerical solution is economical in terms of both computing time and core storage.     

Application of DSISR program to recessed shells of revolution

Application of the DSISR program to recessed shells of revolution is illustrated on the examples of a cylinder with two diametrically-opposite rectangular cutouts and a sphere with a single trapezoidal cutout. The program which is suitable for a wide range of static and dynamic problems was developed for general linear analysis of shells of revolution with arbitrary stiffness and mass density distributions. In the analysis, the equations of motion are derived with the aid of Sanders' theory, and the numerical solution procedure is based on Fourier expansion in the circumferential direction, on finite differences in the meridional direction, and on Houbolt's method in the time domain.     

Finite element elastic-plastic-creep analysis of two-dimensional continuum with temperature dependent material properties

A technique is presented for performing finite element elastic-plastic-creep analysis of two-dimensional continuum composed of material with temperature dependent elastic, plastic, and creep properties. The plastic analysis utilizes the Prandtl-Reuss flow equations assuming isotropic material properties and linear strain-hardening. A power creep flow law formulated by Odquist is used to determine the steady state creep strain rate. The plastic and creep flow laws are employed to derive a ‘softened’ plastic-creep stress-strain matrix. These modified stress-strain relations are then used to formulate the element stiffness matrix in the usual manner. The differences in the elastic, plastic, and creep properties of the material due to the temperature change during the increment result in the formation of pseudo stresses, which in turn lead to load terms that appear on the right hand side of the equilibrium equations. The load terms resulting from these pseudo stresses not only keep the solution on the temperature dependent stress-strain curve of the material, but also correct for the elastic ‘overshoot’ that occurs when an element changes from an elastic to a plastic state. The effect of large displacements is included by the formulation of the geometric stiffness matrix for each element being used in the computer code. With this procedure it becomes economically feasible to perform elastic-plastic-creep stress analysis of two-dimensional continuum subjected to transient thermal and mechanical loadings. Several examples of both elastic-plastic and creep analyses are presented, and the finite element solutions are compared to either other theoretical solutions or experiment.     

键控触发温度标注显微熔点仪研制

显微熔点仪在材料熔点测定、药物鉴别、煤灰熔融性分析等医药化工领域具有重要的应用价值.针对操作者观察熔化状态与记录温度不能同时进行的特点,开发了通过按键触发记录熔化温度的新型熔点仪.考虑恒温控制过程中温度会出现振荡的特性,提出了按设定升温速率动态调整目标温度的分段所列积分微分控制程序,方便操作者在上位机进行自由设定.键控...     

Constitutive modeling of concrete in finite element analysis

Approaches generally used in defining constitutive relations for concrete are reviewed. A computer program developed for the three-dimensional finite element analysis of complex reinforced, prestressed, and refractory concrete systems is described. The constitutive models based on isotropic elastic, orthotropic elastic, and plasticity formulations, which are implemented in that program, are discussed in detail. The program incorporates nonlinear material properties, cracking in concrete, shear transfer in cracked reinforced concrete sections, and time dependent effects such as creep, shrinkage, and transient temperature distributions. A wide range of structural problems are analyzed to demonstrate the applicability of the computer program. Comparisons between predictions with different constitutive models, and between predictions and test results are made.     

Designing screens for people to use easily

The use of interactive computer systems is expanding rapidly. In many applications users can communicate directly with computer-based systems through an interactive dialogue at a display terminal. However, this direct form of communication has created problems. Whereas early users of on-line systems were skilled computer professionals, today's users may have little or no training in computer technology. How then does this group communicate effectively with a computer systems?

The answer is that many users communicate only with considerable difficulty. The result is that the effectiveness of many systems is very much less than expected. The reason for this is simple: these systems are not very good at communicating with their users.

The most common communications bridge between a person and a computer system is a display screen. A well-designed screen format can enhance user productivity, eliminate or reduce user input errors, and promote end user satisfaction. A poorly designed screen has the opposite effect: it will decrease human processing speed, provoke user mistakes, and complicate computer operations.

Screen design requires the same care as designing the overall application. It employs the same techniques as planning and preparing good user documents. Screens, like documents, must be easy to understand and easy to use. To achieve these objectives, screen designers must make good choices regarding three ease-of-use parameters: format; screen content and layout; and style. This paper describes how standards may be established for each of these parameters in a proposed application or system. Futher, an interactive tutorial computer program has been developed (using Bricklin's DEMO program) which may be used to illustrate the application of these standards.     

Thermal analysis of microwave GaN‐HEMTs in conventional and flip‐chip assemblies

Temperature rising which originates from self‐heating degrades the electrical characteristics, reliability, and lifetime of high‐power GaN‐HEMTs. In this article, a systematic analytical approach for thermal evaluation of microwave GaN‐HEMTs is constructed through combining and scrutinizing some of the basic static thermal analysis methods to provide a deeper insight into the process of the channel temperature rising and self‐heating with a much lower computational burden. The proposed systematic thermal analysis has been applied to two different assembly methods: conventional mounting and flip‐chip mounting. Although the mathematical and empirical equations used are simple enough to save time, the effects of several phenomena and different conditions on the channel temperature have been taken into account. These include heat crowding phenomenon, the effect of temperature‐dependent thermal conductivity of the transistor constituent materials, transistor geometry, die‐attach material properties, and bump dimensions. To validate the accuracy of the calculations, all the analytical analyses are followed by 3D thermal simulations in ANSYS software. The simulation results confirm the accuracy of the analytical calculations.     

Program families: Program construction by context independent refinements

The concept of program families is a generalisation of the conventional stepwise refinement paradigm. We formalise program families by allowing Hoare-triplets to be parameterized. Next we derive a simple calculus to develop programs which are known a priori to be correct with respect to explicitly formulated pre- and postconditions.

Program families deal with at least two important problems of conventional refinement steps, i.e. program families are not context dependent and they apply just as well to top-down decomposition as to the bottom-up or middle-out approach. It turns out that the meaning of a pseudostatement in the context of program families is quite different from its meaning in the conventional refinement process.

A couple of examples illustrate the technique: the 1000 primes problem, a palindrome filter and a sorting routine.

The discussion relates program families to Morgan's refinement calculus, Knuth' literate programming and Soloway's programming plans.